The Japan Meteorological Agency raised the warning level for Mount Aso to 3 on a scale of 5, warning hikers and residents not to approach the mountain.
Japanese television broadcast footage of a plume of thick smoke over the volcano, according to the Associated Press.
The warning was issued for Aso and two nearby towns in Kumamoto Prefecture, located in the north-central region of the southern island of Kyushu.
Yoshihiko Isozaki, deputy prime minister of the national government, said he was still gathering information about the blast.
Mount Aso is the largest active volcano in Japan, and one of the largest in the world.
The volcano is located in Aso Kugu National Park, Kumamoto Prefecture, on the island of Kyushu.
The highest peak in the mountain is 1592 meters above sea level
.